1. Field of the Invention
The present invention relates to test facilities for transceiver stations, particularly but not exclusively W-CDMA transceivers for use in mobile communication networks.
2. Description of the Related Art
It is common practice to monitor a transceiver in a base station in order to detect possible malfunctions. If a malfunction occurs during a transceiver""s normal operation, information about the malfunction is reported to the base station controller which can then take the necessary actions in order to limit the harm caused to the base station system or a mobile telephone system. Furthermore it is useful to be able to functionally test a transceiver without connecting it into a mobile telephone network. Particular complications arise in a CDMA system, because it is not possible to definitely determine whether a receive signal is the same as a transmitted signal based just on the input power of the receiver, since all information signals lie on top of each other at the same frequency and, furthermore, received power does not in any event indicate the condition of the digital transmitter parts. While some previous test proposals have used a bit error rate of comparing received bits to transmitted ones, in a CDMA system in order to be able to calculate the bit error rate, the receive signal has to be completely despread. This is a rather complicated process and involves the base-band parts where rake receivers are placed. These parts are typically located separately from the transceiver. Therefore, it is difficult to test transceiver components alone because any results will inevitably be affected by the rate receiver parts used for the despreading.
According to one aspect of the invention there is provided test circuitry for a transceiver comprising: a transmitter for transmitting a test signal incorporating a test spreading code; a receiver for receiving said test signal, said receiver including detecting means set up in accordance with said test spreading code for detecting whether or not signals received by the receiver include the test signal incorporating said test spreading code.
There is also provided a method of carrying out a test in a transceiver, the method comprising: applying a test spreading code to a test signal and transmitting said test signal; feeding back a test sample of said test signal to a receiver; at the receiver, setting up detecting means in accordance with said test spreading code; and detecting whether or not said test sample includes said test signal by checking for a match at said detecting means.
In accordance with the described embodiment, a matched filter is used to determine whether or not the transmitted signal has passed the whole transceiver""s transmitter-receiver chain, without the need to complete despreading functions on the signal. The test spreading code can be a synchronisation code already available in a W-CDMA system. The test method can be used in conjunction with bit error rate measurements, but when it is used on its own it has the advantage that it tests only the transceiver components and does not require passage of the signal through the rake finger parts.
Thus, the described embodiments of the invention have the advantage that a W-CDMA transceiver can be tested without the rake receiver, and the receiver test functions can determine definitely that the received signal is the transmitted one. The synchronisation codes are well defined in a W-CDMA system and readily available, so this test feature does not reduce the capacity of the system.
It is advantageous in a test system of this type to properly control the power level of the test signal. Thus, according to a further aspect of the invention there is provided circuitry for adjusting the power level of a test signal in a transceiver test loop, comprising: a first storage location which holds power control information to be transmitted as an RF signal; a second storage location which, in a normal mode of operation, holds power control information received in an RF signal which is used to control the transmitted power level of the transmitted signal; and a switch for selectively transferring the power control information from the first storage location to the second storage location in a test mode of operation. This aspect of the invention also provides a method for adjusting the power level of a test signal in a transceiver test loop, the method comprising: receiving a test signal and determining a signal to information ratio of said test signal; generating power control information in dependence on said determined signal to information ratio, and loading said power control information into a first storage location; transferring the power control information from said first storage location to a second storage location from which the power control information is used to control the transmitted power level for a subsequent test signal.
It is possible to implement two levels of power control. A long term automatic gain control can be implemented by using some sort of previous knowledge of conversion loss of the test loop, based on calibration data, transmitted mean power and receiver mean power. This can be implemented by an attenuator on the receive side which attenuates the fed-back test sample.
In addition, a so-called fast automatic gain control can be implemented using the method and circuitry as hereinabove defined. In normal operation, the first storage location holds the downlink power control bit for transmission to a mobile station, while the second storage location holds the uplink power control bit which is normally received from the mobile station and used to adjust downlink power. According to the embodiment of the invention described herein, a swapping method is used to change the uplink AGC bit to adjust the downlink power in a test loop.
A further aspect of the invention provides a transceiver for implementing a test loop, the transceiver comprising: a receiving mixer for converting a test signal from a transmitting frequency to a receiving frequency; a local oscillator for generating a conversion signal for the mixer; a first power adjustment means for adjusting the power level of the received test signal prior to conversion of the mixer; and a second power adjustment means for adjusting the power level of the transmitted test signal based on the signal to information ratio of the received test signal.